A serving is the amount of food recommended in consumer education materials such as MyPlate. A portion is the amount of a food you choose to eat at any one time â which may be more or less than a serving. Here are some everyday comparisons to help you figure out your serving sizes. 1  1 teaspoon of margarine is the size of one dice. 2  3 ounces of meat is the size of a deck of cards. 3  1 cup of pasta is the size of a baseball. 4  1Â½ ounces of cheese is the size of four stacked dice.
Oxygen: Specialized nerve cells within the aorta and carotid arteries called peripheral chemoreceptors monitor the oxygen concentration of the blood and feed back on the respiratory centers.
1 The increased rate of breathing returns the carbon dioxide concentration to normal and the breathing rate then slows down. 2  Hydrogen ion (pH): The peripheral and central chemoreceptors are also sensitive to the pH of the blood and CSF.